Study Of Polyurethane Modified By HDI Trimer-Isocyanate Group-containing Siloxane Complex

Polyurethane (PU) coating with desirable performances has been widely used in industrial and civil fields. The diisocyanate trimer that can help to promote the formation of the internal cross-linked structure in PU coating film, thereby improve its performances has become one of the main raw materials for the preparation of PU coating. Currently, toluene diisocyanate (TDI) trimers have already occupied a large proportion of diisocyanate trimers for PU. However, TDI trimer is prone to the chemical change to quinoid structure caused by ultraviolet radiation resulting in yelling of PU coating film which will affect its appearance and stability. Therefore, the aliphatic diisocyanate trimers like hexamethylene diisocyanate (HDI) trimer have been paid more and more attention. HDI trimer without the chormophoric group from conjugated system is more resistant to PU film yellowing. On the other hand, for HDI trimer. the lack of rigid aromatic cyclic structure may lead to some unfavorable effects on the performances of PU coating such as mechanical properties, hardness, water resistance and so on. Therefore, for the purpose of improving coating performances, it is necessary to pursue an effective way to modify HDI trimer.In our work, HDI trimer was modified by 3-Isocyanatopropyl-triethoxysilane (IPTS), and the HDI trimer-isocyanate group-containing siloxane complex was obtained. This complex was utilized to modify the solvent-based and waterborne PU coating respectively. The synthetic procedure was optimized. The chemical structure of PU products were confirmed by infrared spectrum analysis, meanwhile, the thermogravimetric analysis was also performed. Additionally, the performances of coating including the water, acid and alkali resistance, hardness, adhesion, yellowing resistance, viscosity, mechanical properties and the particle size distribution of PU emulsion were all investigated.The experimental results suggested that the desirable coating performances were achieved by introducing the HDI trimer-isocyanate group-containing siloxane complex into PU coating. This research has laid a foundation for the subsequent industrial production and application of the related PU products.